It is common experience that a chair or a table will not rest firmly on the floor. The problem is usually attributable to a difference in the plane reached by the ends of the chair legs. A difference of a small fraction of an inch is readily sensed in that the four-legged table will not rest stably in position. A cummulative error is attributable to the floor. If the base of the table or chair is a disk, or rug, the error is also sensed. That is, there can be differences in the plane of the floor within the area spanned by the table or chair feet or base, which differences are sensed by the user of the table, or the chair, through a rocking of the table or the chair. Improvisations are many. The usual one in a restaurant is a match book or folded napkin slipped under a table leg. Corrections if left to the cabinet maker are difficult because it is necessary to bring the item to a work shop and level it accurately there. This has the attendant disadvantage that this kind of precision work can easily be destroyed in the process of redelivering the table or chair to its place of use. Rough handling, a slight distortion of a joint, and the error is as bad as it ever was.
It is the basic object of the invention to promote a device useful under tables, chairs, etc., to correct automatically for errors in the level of the device or plane.